Catalytically promoted methods for the conversion of crude hydrocarbons into commercial products include cracking, hydrocracking, reforming, hydroforming, coking, desulfurizing, denitrogenation, etc. Such reactions generally are performed at elevated temperatures, for example, about 150.degree. to 750.degree. C., more often 300.degree. -650.degree. C. Feedstocks for these processes normally comprise liquid and solid hydrocarbons which at the temperature of the conversion reaction are generally in the fluid, i.e., liquid or vapor state and the products of the conversion frequently are lower boiling materials. In particular, hydrogen treating of hydrocarbons is widely practiced and typically uses a catalyst consisting of cobalt and molybdenum supported on alumina.
The typical feedstock subject to catalytic conversion contains a variety of metals, one being vanadium. These metals, present in the feedstock, deposit on the catalyst and as a consequence catalytic activity and efficiency is lost. These metals deposit as a nonvolatile compound on the catalyst during the conversion process so that the standard regeneration processes practiced to remove coke do not remove these metals. Also, removal of coke by high temperature treatment with oxygen cannot be done since such treatment in the presence of vanadium reduces the catalytic surface area.
Metal poisoning of cracking catalysts is a major cost item in present day refining and is a bottleneck in upgrading residual stocks. Current methods of combating metal poisoning are careful preparation of feedstocks to keep metal content low and periodic replacement of catalyst to control metal levels on the catalyst. This method of controlling metal levels by catalyst replacement, however, is marked by substantial increased costs per unit of product produced.
Catalysts used commercially are the result of years of study and research into the nature of the hydrogen treating process, and the costs are not negligible. Thus, catalyst cost frequently dictates the nature of the feedstream used. Feedstocks, which are plentiful but which have high metal content, are frequently avoided merely because their use would dictate frequent changes of expensive catalyst.
To reduce this cost, alternative methods for controlling metal poison concentration on catalysts are demetallization processes which avoid the step of catalyst discard and, therefore, circumvent any objection to the use of these plentiful, but metal contaminated, petroleum feedstreams.
However, in practicing demetallization, it is imperative that the process utilized is not complicated or requires the setting up of apparatus equivalent to that used in original catalyst manufacture. It is also an essential criterion that the contaminating components be removed without removing the expensive catalytic components.